A former top strategist for Ronald Reagan has defected from the camp of the pre-season GOP front-runner to become political director of George Bush's uphill effort to win the 1980 Republican presidential nomination.

David Keene confirmed that he left Reagan -- not because of disenchantment with the candidate but because he lost an intra-staff struggle for a top job and did not want to accept a lesser position in the Reagan campaign.

In the Bush campaign, Keene, who still calls himself very much a conservative, will find himself working alongside old adversaries.

Bush's press secretary, it has been learned, will be Peter Teeley, a party liberal who was once press secretary to Sen. Jacob Javits (R-N.Y.) and is now director of communications for the Republican National Committee.

And the core of the Bush organization is the brain trust of former president Ford's 1976 campaign, which came close to being derailed by Keene and his Reagan colleagues. Ford's campaign chairman, James Baker, is now serving the same role for Bush, as is Ford's pollster and adviser on public opinion, Robert Teeter.

Keene will have the title of deputy chairman for operations in the Bush campaign. In 1976, he was director of Reagan's southern region effort.

Keene conceded in an interview that Reagan is his first choice for president in 1980. "That's fair to say," he said. "It's the truth. I like Reagan and I think he'd be a good president... but there's some question as to whether he can win."

"I think Bush is pretty conservative," Keene said. "And after checking with conservatives around the country for the past three weeks, I learned that although Reagan is their first choice there was some feeling that Reagan may not make it -- and that Bush is considered by them as a good second choice.

"At this point, the nomination is Reagan's to lose. He's the front-runner. He's way ahead in the polls and Bush is rated low... If Reagan is going to lose he's got to blow it: make a mistake during the campaign, say the wrong thing."

Keene added that Reagan's age will be a factor.

Bush, in Houston, said it did not bother him to be considered second choice behind Reagan by his own political director.

"I couldn't care less," Bush said. "The fact that Dave Keene worked for Reagan is a political dividend -- so much the better... I wanted ability and he's the best."

Bush considers it a distinct plus to be adding both an ex-Reagan man (Keene) and an ex-Javits man (Teeley) to his inner circle. "I don't want to draw from just one segment of the party," Bush said. "I'm not going to try to label myself. You've got to figure that out as the campaign goes along."

While Keene labels Bush a "conservative," Peter Teeley sees Bush as "in the moderate-to-conservative mold... His strength is that he is able to attract people across the Republican spectrum -- conservatives like David and more moderate people like myself."

Recent polls have shown that both Ford and Reagan are rated way ahead of the rest of the field as favorites for the GOP presidential nomination in these early pre-campaign days, both scoring in the 30s. Reagan people make it clear that Reagan intends to seek the nomination; Ford, however, is widely considered disinclined to run.

Bush is listed at around 3 percent in the polls. But his strategists comfort themselves by observing, as campaign chairman Baker did yesterday, that, "If you looked at Jimmy Carter this time in 1975 you hardly would have found him even listed in any of the polls."